Injury mitigation system for power tools

ABSTRACT

A power tool comprises a detection system for detecting a situation where an operator using a power tool of the type which has an exposed rotating component contacts the rotating component, and a protection system for minimizing the possibility of an operator being injured by contacting the rotating component.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to Provisional Application No.60/902,196 titled “Injury Mitigation System for Power Tools” filed onFeb. 20, 2007, Provisional Application No. 60/902,195 titled “DecouplingMechanism for Power Tools” filed on Feb. 20, 2007, and ProvisionalApplication No. 60/922,486 titled “Clutch for Injury Mitigation Systemfor Power Tools” filed on Apr. 9, 2007, which are specificallyincorporated by reference.

BACKGROUND OF THE INVENTION

The present invention generally relates to power tools, and moreparticularly, to safety detection and protection systems for power toolssuch as circular saws of the type that are used for cutting wood andother materials.

For as long as power tools have existed, there has been concern for thesafety of those who operate them. This is particularly true with regardto power tools of the type which have relatively large exposed movingblades that can easily cause serious injury to individuals whocarelessly use the tool or who are the victim of a true accident thatresults from unforeseen conditions. While safety systems have beendeveloped for machine tools and other commercial tools, such as stampingtools, punch presses and other machines which exert great force inmanufacturing metal and other parts, such systems often have a level ofsophistication and complexity that is achieved only at a cost that isprohibitive if considered for use in tools that are marketed toindividual consumers or small contractors and tradesmen.

More particularly, the well known circular saw that is used bywoodworkers and tradesmen has a rotating blade that can be exposedduring use even though blade guards have been provided with such sawswhen sold for the last several decades. Such blade guards, whileeffective to prevent some injuries, are considered unwieldy by manyoperators. In fact, many operators find that such blade guards actuallyinterfere with the use of the circular saws and therefore remove suchblade guards most of the time. Obviously, a rotating circular saw bladecan cause great injury to an operator and countless hand injuries occurannually because of careless use or the occurrence of fortuitousaccidents.

Safety systems have been developed for use on saws to stop the bladewhen the operator's hand approaches the blade and which trigger a brakemechanism that typically includes a pawl structure that is urged intothe blade by a biasing mechanism that is retained by a fusible memberthat is melted by a high energy electrical current. Severing the fusiblemember releases the pawl to stop the blade, or in some embodimentscauses the blade to be retracted down below the work surface in the caseof the system being utilized with a table saw. All of these systems haveone or more disadvantages in terms of cost, convenience of use, earlyand effective detection of a dangerous condition and the ability toprovide graduated protective actions as a function of thecharacteristics that develop during a potentially dangerous condition.Further, many protection systems are destructive to the blade to theextent that the blade must be replaced after a braking event.

SUMMARY OF THE INVENTION

The saw comprises a detection system for detecting a situation where anoperator using a power tool of the type which has an exposed bladecontacts the blade, and a protection system for minimizing thepossibility of an operator being injured by contacting the blade.

In an embodiment, a detection system for a saw having a blade and atrigger that is depressed by a user to operate the saw is provided. Thedetection system includes an optoisolator circuit configured forisolating a high voltage input from a power supply at a first part ofthe power tool, and for applying a lower voltage to a second part of thepower tool to provide a differential in voltages on the power tool. Asensor is configured for sensing a change in voltage on the second partof the power tool when the user contacts the rotating component. Whenthe sensor senses the voltage change for a predetermined duration, thesensor emits an actuating signal to actuate a solenoid or a relay.

In one embodiment, a braking mechanism for a power tool having arotating component includes a brake actuation mechanism and a brakecaliper mechanism. The brake actuation mechanism includes a solenoid ora relay mounted on a frame having at least one linkage and a releasablestructure attached to the linkage. The brake caliper mechanism includesa first portion for slidingly receiving a first caliper member, and asecond portion having a second caliper member. When the first calipermember is received in the first portion, the first caliper member andthe second caliper member are configured to be generally parallel and tooppose each other on each side of the blade. When the solenoid or relayis actuated, the solenoid removes the releasable structure fromengagement with the first caliper member to permit the first calipermember to extend towards the second caliper member under spring force.

In an embodiment, a stopping mechanism for a power tool having arotating component includes a gear fixed to rotate with the rotatingcomponent having a first surface and at least one detent, where a firstend of the detent has a receiving structure. At least one latch having amoveable member is slidably mounted in a fixed but pivotable tube. Themoveable member has a hook structure and is configured to engage thereceiving structure of the detent. An actuator pivots the latch toposition the hook structure into range of the detent, where the hookstructure engages with the receiving structure and stops the rotation ofthe rotating component.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a circular saw having an injury mitigationsystem of the present invention including a detection system and aprotection system.

FIG. 2. is an electrical schematic diagram of representative circuitryfor the detection system.

FIG. 3 is an exploded view of a braking mechanism including a side viewof a brake actuation mechanism and a top view of a first caliper member.

FIG. 4 is an exploded view of the full mechanical braking mechanismincluding a top view of the brake actuation mechanism, a top view of thefirst caliper member, and a top view of the caliper brake mechanism.

FIG. 5 is a side view of the caliper brake mechanism including first andsecond caliper members.

FIG. 6 is a side plan view of the brake actuation mechanism and thefirst caliper member mounted in the brake actuation mechanism.

FIG. 7 is a side view of a stopping mechanism including a gear and alatch.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE PRESENT INVENTION

Briefly stated, the present injury mitigation system will be shown anddescribed with various embodiments of a detection system as well asvarious embodiments of a protection system that can operate to mitigateinjury to the tissue of an operator during operation of a power tool.While the embodiments that are illustrated and described herein comprisesystems for a circular saw, it should be understood to those of ordinaryskill in the art that the detection system as well as aspects of theprotection systems are applicable to other power tools. The invention isalso applicable to other broader applications that may be implemented invarious industries and endeavors. Shop tools other than circular sawsare particularly capable of having detection and protection systemsadapted for their use, using the concepts and principles of theembodiments shown and described herein.

Generally, the detection system senses when an operator makes contactwith the blade and initiates the protection system. The protectionsystem preferably initiates a braking mechanism and a stopping mechanismso that the blade will stop rapidly.

Referring now to FIG. 1, a representative circular saw is indicatedgenerally at 10 and includes a motor 12 disposed in a motor housing 14,which is used to rotate a blade 16 housed in an upper protective guard18 and a lower guard 20. A handle 22 extends from the motor housing 14and includes a trigger 24 and a power cord 26. A base plate 28 isgenerally transverse to the blade 16 and extends around the blade.

Referring now to FIG. 2, the detection system 30 will be described. Thedetection system 30 is configured to detect when an operator makescontact with the blade 16, and to initiate the protection system. For aneffective detection system 30, it is necessary that the detection of theoperator's contact with the blade 16, as well as the generation of anactuating signal to the protection system, be done in a very short time.While the amount of time can vary upwardly or downwardly depending uponthe nature of operation of the detecting system 30 and specificoperation conditions, generally the faster the operation of thedetection system the better.

In order to operate a circular saw 10, the operator must constantly holdthe trigger 24 down. The present detection system 30 operates byapplying a voltage to the trigger plate 24A of the saw. The trigger 24includes circuitry which is capable of detecting the absence of avoltage on the trigger. When the operator's body comes into contact withthe blade 16 (such as with the operator's fingers), the operator's bodyshorts the voltage on the trigger 24A to ground. In other words, theoperator's body completes the circuit to ground by touching the blade16.

The missing voltage on the trigger plate 24A is detected by a timingcircuit or sensor 32 (preferably a 555 timer), which emits an actuatingsignal to activate a transistor switch 34 (preferably a Darlington typetransistor or relay), which energizes a solenoid or relay 36 to actuatea braking mechanism. It is contemplated that the solenoid 36 can beenergized in response to a measured predetermined duration of theabsence of applied voltage to the trigger plate 24A.

In the preferred embodiment, +15 volts is constantly applied through theoperator's body by the operator's finger making contact with the triggerplate 24A. It is contemplated that other voltages can be used that arerelatively comfortable for the user. When the operator shorts theelectricity to ground, the 555 timer 32 senses a drop in voltage on thetrigger. When the 555 timer 32 senses the drop in voltage, it sends a+15 volt output charge to activate the Darlington transistor 34. TheDarlington transistor 34 acts as a switch for the solenoid 36 to releasethe braking mechanism on the blade 16.

With regard to the specific circuitry that is used in the preferredembodiment of detection system 30, the electrical schematic diagram ofrepresentative circuitry is shown in FIG. 2. The following descriptionrefers to the preferred circuitry of FIG. 2.

To run a safe voltage to the operator through the trigger plate 24A, thedangerous voltages running to the saw 10 are isolated from the operator.When the dangerous high voltage is isolated, the operator is able tocontact the trigger to complete part of the circuit at a relatively lowvoltage. In the preferred embodiment, this isolation is accomplished bymaking an optiosolator circuit, indicated generally at 40, whichisolates the high voltage (input from the 110V socket 44) from the lowvoltage (input from a 30V adapter 42).

The optoisolator circuit 40 uses an extension of the main power wireusing 14 AWG wire with #10 solderless terminals for connections. A 43Ωresistor (R5), 01 μF capacitor (C4), and a snubberless 600 V, 25 A TRIAC(TR1) are wired to the optoisolator extension in the circuit. A TRIAC(Triode or relay for alternating current) is a bidirectional electronicswitch that can conduct current in either direction when it istriggered. From the snubberless TRIAC (TR1), a 0.056 μF (C5), a 360Ωresistor (R4) are wired to pin 6 of the optoisolator TRIAC-output 6 DIP.The snubberless TRIAC is wired to pin 4 of the optoisolatorTRIAC-output. Pin 1 of the optoisolator TRIAC-output (40) is preferablyconnected to a 2×0.5×0.02″ copper sheet molded around the trigger 24forming the trigger plate 24A, preferably with a #10 solderless terminaland #4-40×¼″ round head slotted zinc bolt and nut. The trigger ispreferably wired to pin 2 on the precision 555 timer 8-DIP. Pin 2 on theoptoisolator TRIAC-output (40) is preferably connected to pin 3 on the555 timer 32.

In the preferred embodiment, the power of a 30 V 400 mA, AC to DCadaptor (32) is emitted through 22 AWG four wire shielded communicationswire to a 5 V, 1A zenor diode (46) before reaching a +15V, 1A voltageregulator (48) for the low-voltage electrical components. While a 400 mApower supply 42 is incorporated, it is contemplated that other powersupplies can be used. Preferably, 18-AWG four wire shieldedcommunications wire is used to connect the touch switch to 18-DIP and8-DIP sockets containing: the 555 timer (32), 0.01 μF capacitor one(C1), 15 μF (C2), 0.01 μF (C3), 20 KΩ resistor one (R1), 312Ω (R2), 1 MΩ(R3), and the NPN 100 V Darlington transistor (34). A 22-AWG four wireshielded communications wire runs from the adaptor (32) and the 555timer (32) and base of the Darlington transistor (34) to the 0.75″diameter 28 VDC tubular solenoid (36). The solenoid (36) is attached toa grounded bolt with a #12 solderless terminal.

When the voltage on the trigger decreases, the optoisolator 40 willpreferably shut down the TRIAC (TR1). In turn, the TRIAC (TR1) willpreferably shut down the power to the motor 12.

Referring now to FIGS. 3-6, the detection system 30 is used to actuate abraking mechanism, indicated generally at 50, to initiate braking of theblade 16. Preferably, the braking mechanism 50 is configured tocompletely stop the blade 16 within 0.05 seconds of the operatorcontacting the blade.

The braking mechanism 50 includes a caliper brake mechanism indicatedgenerally at 52, and a brake actuation mechanism indicated generally at54. The brake actuation mechanism 54 includes the solenoid 36 of thedetection system, which actuates the caliper brake mechanism 52 to clampdown onto the blade 16. Preferably, the caliper brake mechanism 52clamps down onto the blade 16 generally near the periphery of the blade,but generally radially inward from the teeth of the blade.

The caliper brake mechanism 52 is generally “C”-shaped with a firstportion 56 including a tube 58 for slidingly receiving a first calipermember 60, a second portion 62 including a second caliper member 64, anda tube 66 located therebetween. When the first caliper member 60 isdisposed in the tube 58, the first caliper member 60 and the secondcaliper member 62 are generally coaxial and oppose each other.

The first caliper member 60 includes a rod 68 having a proximal end 70and a distal end 72. The proximal end 70 has an extension member 74 thatextends from the rod 68 and an engaging structure 76 generallytransverse to the rod. A retainer member 75 is preferably slidingly andconcentrically disposed on the rod 68 beneath the extension member 74.The retainer member 75 prevents the displacement of a concentricallydisposed compression spring 78 to the extension member 74.

The compression spring 78 extends down into a cylindrical casing 80 thatis concentrically disposed around the rod 68. Inside the casing 80, therod 68 is attached to a generally cylindrical rubber stopper 82 thatprotrudes from the casing. The rod 68, the casing 80 and the rubberstopper 82 preferably have a static relationship to each other.

The proximal end 70 of the first caliper member 60 is mounted into thebrake actuation mechanism 54. The brake actuation mechanism 54 includesa generally “L”-shaped frame 84 having a retention bracket 86. Theretention bracket 86 includes a receiving structure 88 for receiving theretainer member 75 of the first caliper member 60, which is placedunderneath the retention bracket 86.

When the retainer member 75 is in the receiving structure 88, theproximal end 70 of the first caliper member 60 is pulled upwards againstspring force as the retainer member is slid downwardly along the rod 68,until the engaging structure 76 of the first caliper member 60 isreceived in a releasable structure 90 of the brake actuation mechanism54. The releasable structure 90 holds the proximal end 70 extended fromthe retainer member 75 against spring force.

The releasable structure 90 is on at least one, and preferably aplurality of linkages 92 that are attached to the frame 84 of the brakeactuation mechanism 54. The releasable structure 90 is generally low infriction and allows the first caliper member 60 to be slidinglyreleased. A lever member 87 is actuated by the solenoid 36 to move thelinkages 92. In this configuration, the detection system of FIG. 2actuates the brake actuation mechanism 54 to let out the compressionspring by a signal to the solenoid 36 to pull in. When the linkages 92are moved by the solenoid 36 pulling in on the lever member 87, thereleasable structure 90 pivots out from under the engaging structure 76to release the compression on the compression spring 78. When thereleasable structure 90 is pivoted, the first caliper member 60 is freeto displace downward, and is pulled by the compression spring pullingagainst the retention bracket 86.

The distal end 72 of the first caliper member 60 is slidably receivedinto the tube 58. When the engaging structure 76 is released from thereleasable structure 90, the rod 68 slidingly extends from the tube 58and engages the saw blade 16. When the engaging structure 76 is releasedfrom the releasable structure 90, the potential energy stored on thecompression spring 78 is exerted on one side of the saw blade 16.Substantially simultaneously, the “C”-shaped brake mechanism 52displaces with respect to the stationary tube 66 in the directionindicated in FIG. 5. When the first and second portions 56, 62 displace,the second caliper member 64 engages the blade 16 at the opposite sideof the blade from the first caliper member 60.

The caliper brake mechanism 52 grips the saw blade 16 between the firstcaliper member 60 and the second caliper member 64. The rubber stoppers82, preferably made of black neoprene with a flat head, are preferablydisposed at the distal ends of both the first and the second calipermembers 60, 64 to provide additional frictional resistance. Since boththe first and the second caliper members 60, 64 grip the blade 16 atopposing surfaces, the blade is not bent by the brake mechanism 52during a braking event.

In one particular embodiment, about 0.25 inches of the total springcompression is used through the extension of the first caliper member 60of about 0.125 inches of air space on each side of the blade 16, leavingabout 0.25 inches of the spring compression to stop the blade byapplying pressure onto the blade. When the brake mechanism 50 isdeployed according to this embodiment, the blade 16 should completelystop within less than 0.1 seconds, and preferably within 0.05 seconds,of the operator contacting the blade. It should be understood that thenumeric values of this specific embodiment are given only as an example,and the invention should not be limited by these values.

The braking mechanism 50 such that the blade 16 extends between thefirst and the second caliper members 60, 64. It is contemplated that thebraking mechanism 50 can be attached with the bolt that connects thelower shield to the saw 10. Further, in an alternate embodiment to adisplacing brake mechanism, the first and second portions 56, 62 of the“C”-shape brake mechanism 52 can pivot inwardly with respect to eachother to engage the rubber stoppers 82 on each side of the blade 16.

A stopping mechanism, indicated generally at 94, can be used in tandemwith, or in place of the braking mechanism 50. Referring now to FIG. 7,the stopping mechanism 94 includes a gear 96 that is static with respectto the blade 16, i.e. rotates with the blade. The stopping mechanism 94also includes a pivoting latch 98 mounted adjacent the gear 96. A topsurface 100 of the gear 96 is generally planar and has detents 102formed into the surface. The detents 102 are configured to engage with afirst end 104 of the pivoting latch 98.

The gear 96 rotates with the blade 16 in the clockwise direction asdepicted in FIG. 7. In the preferred embodiment, there are four detents102 that have a curved shape including a smaller end 106 that graduallyincreases to a larger end 108. The larger end 108 has a generallyconcave receiving structure 110.

The pivoting latch 98 includes a moveable member 112 having a first leg114 and a second leg 116 that is slidingly disposed through a tube 118.On the first leg 114, the moveable member 112 includes a hook structure120 having a corresponding and generally convex shape to the generallyconcave receiving structure 110. In this configuration, the receivingstructure 110 and the hook structure 120 of the pivoting latch 98 areconfigured to engage each other such that when the pivoting latch islowered into range of the gear 96, the pivoting latch will be pulledunder and locked into the receiving structure 110 of the detent 102.

On the second leg 116, a coil spring 122 encircles the moveable member112. The tube 118 is preferably attached to the saw 10 and is pivotableto allow the pivoting latch 98 to pivot towards the gear 96 upon beingactuated.

In the first, top position in FIG. 7, the pivoting latch 98 is generallytangential to the gear 96 and is restrained from engaging with the gearwith an electromagnet (not shown), however other actuators arecontemplated such as a solenoid actuator. Further, it is contemplatedthat the solenoid 36 of the detection system 30 can actuate the stoppingmechanism 94.

In the second, side position of the pivoting latch 98 in FIG. 7, thecurrent running through the electromagnet is reversed, switching thepoles, and moving the pivoting latch so that the hook structure 120 isengaged into the detent 102 and locked by the receiving structure 110.As the gear 96 rotates, the pivoting latch 98 is pivoted to orientitself at an angle to engage the gear at.

In the third, bottom position in FIG. 7, the pivoting latch 98 continuesto pivot as the hook structure 120 is engaged. To dampen the relativelyabrupt stop of the blade 16, the moveable member 112 is pulled throughthe tube 118 while compressing the coil spring 122 between a second end124 of the pivoting latch 98 and the tube. When the compression of thecoil spring 122 is at a maximum compression, the blade 16 stops. Thecoil spring 122 will recoil and send the blade 16 spinning in thereverse direction (counterclockwise direction as depicted in FIG. 7)while unlatching and resetting the stopping mechanism 94.

It is contemplated that a pin or other mechanism can be used to preventthe recoil and the spinning of the blade 16 in the opposite direction.It is also contemplated that instead of detents 102 in the top surface100, that the detents can be cut-away or removed.

As discussed with respect to one specific embodiment of the brakingmechanism 50, approximately 0.25 inches of coil spring compression isused to displace the first caliper member 60 to clamp the blade 16between the first and the second caliper members 64. The remainingapproximately 0.25 inches of coil spring compression (after using thefirst 0.25 inches through air space) causes the braking mechanism 50 toapply pressure to the blade 16. It should be understood that the numericvalues of this specific embodiment are given only as an example, and theinvention should not be limited by these values.

When the detection system 30 senses an operator's contact with the blade16, the detection system initiates a protection system. The protectionsystem is configured to stop the blade 16, and preferably includes thebraking mechanism 50 and the stopping mechanism 94, although theprotection system can include additional mechanisms or can exclude atleast one of the braking mechanism and the stopping mechanism.

While various embodiments of the present invention have been shown anddescribed, it should be understood that other modifications,substitutions and alternatives are apparent to one of ordinary skill inthe art. Such modifications, substitutions and alternatives can be madewithout departing from the spirit and scope of the invention, whichshould be determined from the appended claims.

Various features of the invention are set forth in the following claims.

1. A detection system for a power tool having a rotating component and atrigger that is depressed by a user to operate the power tool,comprising: an optoisolator circuit configured for isolating a highvoltage input from a power supply at a first part of the power tool, andfor applying a lower voltage to a trigger plate of the power tool toprovide a differential in voltages on the power tool; a sensorconfigured for sensing a change in voltage on said trigger plate of thepower tool when the user contacts the rotating component; wherein whensaid sensor senses said voltage change for a predetermined duration,said sensor emits an actuating signal to actuate a solenoid or a relay.2. The detection system of claim 1 wherein upon sensing said voltagechange, said optoisolator circuit is opened to turn off a motor of thepower tool.
 3. The detection system of claim 1 wherein said optoisolatorcircuit comprises a Triode or a relay for alternating current switch. 4.The detection system of claim 1 wherein said sensor comprises a timingcircuit.
 5. The detection system of claim 1 wherein said sensor emitssaid actuating signal to activate a transistor or a relay, whichenergizes said solenoid.
 6. A braking mechanism for a power tool havinga rotating component comprising: a brake actuation mechanism including asolenoid or a relay mounted on a frame having at least one linkage and areleasable structure attached to said at least one linkage; a brakecaliper mechanism including a first portion for slidingly receiving afirst caliper member, and a second portion having a second calipermember, wherein said first caliper member is received in said firstportion, and said first caliper member and said second caliper memberare configured to oppose each other on each side of the rotatingcomponent; wherein when said solenoid or relay is actuated, saidsolenoid or relay removes said releasable structure from engagement withsaid first caliper member to permit said first caliper member to extendtowards said second caliper member under spring force from a coilspring.
 7. The braking mechanism of claim 6 wherein said first calipermember comprises: a rod having a first end and a second end, wherein acoil spring is disposed around said second end of said rod; an engagingstructure generally transverse to said rod and disposed at said firstend; and a retainer member slidingly disposed around said rod forpreventing the displacement of said coil spring to said first end. 8.The braking mechanism of claim 7 wherein said first caliper memberfurther comprises: a stopper member disposed at second end of said rodand configured for engaging the rotating component; and a casingconcentrically disposed around said rod and said stopper member.
 9. Thebraking mechanism of claim 7 wherein said frame of said brake actuationmechanism comprises a receiving structure for receiving said retainermember of said first caliper member, wherein when said engagingstructure of said first caliper member is engaged with said releasablestructure and said retainer member is engaged with said receivingstructure, said coil spring is compressed.
 10. The braking mechanism ofclaim 9 wherein said releasable structure pivots to release said firstcaliper member to displace in the axial direction of said rod underspring force, and said first caliper member extends through a tube togrip the rotating component between said first caliper member and saidsecond caliper member.
 11. A stopping mechanism for a power tool havinga rotating component comprising: a gear fixed to rotate with therotating component having a first surface and at least one detent,wherein a first end of said detent has a receiving structure; at leastone latch having a moveable member slidably mounted in a fixed butpivotable tube, said moveable member having a hook structure configuredto engage said receiving structure of said detent; wherein an actuatorpivots said latch to position said hook structure into range of saiddetent, wherein said hook structure engages with said receivingstructure and stops the rotation of the rotating component.
 12. Thestopping mechanism of claim 11 wherein said moveable member comprises afirst leg extending from a first side of said tube, and a second legextending from a second side of said tube, wherein a spring member isdisposed on said second leg and said hook structure is disposed on saidfirst leg.
 13. The stopping mechanism of claim 12 wherein when said hookstructure is engaged with said receiving structure, said gear continuesto rotate and to pull said moveable member, wherein said moveable memberis configured to slide through said tube and to compress said springmember between an end of said second leg and said tube to dampen thestopping of the rotating component.
 14. The stopping mechanism of claim11 wherein said receiving structure has a generally concave shape, andsaid hook structure has a corresponding and generally opposite convexshape.
 15. The stopping mechanism of claim 11 wherein said at least onedetent comprises four detents disposed equidistantly and annularlyaround a peripheral edge of said gear.
 16. A power tool comprising: arotatable member operable upon a user depressing a trigger; a detectionsystem comprising: an optoisolator circuit configured for isolating ahigh voltage input and for applying a lower voltage to the trigger; asensor configured for sensing the decrease of said lower voltage on atrigger plate of said trigger when the user contacts said rotatingcomponent, said sensor emitting an actuating signal to actuate asolenoid; and a protection system comprising: a braking mechanism havinga first caliper member slidingly received in a tube that, upon actuationby said solenoid, extends to engage said rotating component generallyperpendicularly.